1. Field of the Invention
This invention relates generally to storage, separation and analysis of ions according to ion mobilities and mass-to-charge ratios, in the same device, of charged particles and charged particles derived from atoms, molecules, particles, sub-atomic particles and ions. More specifically, the present invention is a single device that enables ion trap mass spectrometry (ITMS) and ion mobility spectrometry, such as high-field asymmetric ion mobility spectrometry or FAIMS, differential mobility, cross-flow ion mobility spectrometry to be performed in a single device, and in any sequence, to thereby perform both types of separation wherein at least two uniquely different chemical-specific identifiers can be obtained to provide identification of the ions.
2. Description of the Related Art
The trapping, separation, ejection and analysis of ions according to ion mobilities and mass-to-charge ratios have always been performed in two distinct devices that perform the operations of ion mobility spectrometry and mass spectrometry. Thus, if it is desired to sequentially analyze the sample using both procedures, it has been necessary to provide separate devices that are in some manner connected in series so that ions can travel from one device to the other.
There are at least several obvious disadvantages to such a serial configuration of devices. First, the operations that can be performed are limited to the specific order in which the devices have been disposed. Second, two distinct devices have always been required, thereby increasing complexity, size and cost of the overall system. Third, there is typically some loss of ions as they travel from one device to another for the different operations to be performed.
To understand the advantages of the present invention and understand how they can be combined in a single device, it is useful to briefly examine the state of the art of both mass spectrometry and ion mobility spectrometry.
Beginning with mass spectrometry, it is a popular instrumental method for analyzing ions. In mass spectrometry, ions are separated according to their mass-to-charge ratios in various fields, such as magnetic, electric, and quadrupole. One type of quadrupole mass spectrometer is an ion trap. Several variations of ion trap mass spectrometers have been developed for analyzing ions. These devices include hyperbolic configurations, as well as Paul, dynamic Penning, and dynamic Kingdon traps. In all of these devices, ions are collected and held in a trap by an oscillating electric field. Changes in the properties of the oscillating electric field, such as amplitude, frequency, superposition of a DC field and other methods can be used to cause the ions to be selectively ejected from the trap to a detector according to the mass-to-charge ratios of the ions.
It is noted that one particular advantage of ion trap mass spectrometers is that these devices typically do not require as high a vacuum within which to operate as other types of mass spectrometers. In fact, the performance of the ion trap mass spectrometer can be improved due to collisional dampening effects from the background gas that is present. Ion trap mass spectrometers typically operate best at pressures in the mTorr range.
The other relevant method of ion analysis is ion mobility spectrometry. Ion mobility spectrometry is becoming increasingly important as an instrumental analytical chemistry technique for separating ions that are created from charged particles and charged particles derived from atoms, molecules, particles, sub-atomic particles and ions.
The basic principle of ion mobility spectrometry is that ions in a gas that are exposed to an electric field travel along the electric field lines at a velocity that is a function of the ion mobility constant K, and the electric field intensity E.
Conventionally, high-field asymmetric ion mobility spectrometry (FAIMS) is a form of ion mobility spectrometry that separates ions based on the combination of their low field and their high field ion mobilities. At a constant gas velocity, the dependence of the ion mobility coefficient is defined by Equation 1:K(E)=K0[1+α(E)]where K0=K(E) at zero electric field and α(E) accounts for the dependence of the mobility coefficient on E at a constant gas density.
If an asymmetric periodic electric field E(t) is applied to a mixture of ions in a gas with certain conditions, an asymmetric waveform is obtained where T=t1+t2, where T is the field changing period. The effect of this field is that ions will oscillate in the gas with a period T. The velocity of each ion during t1 and t2 depends on the amplitudes of Emax and Emin, respectively, and the magnitude of α(E). As a result, the ions will be displaced along the field lines when their α(E) values are different.
When discussing FAIMS, it is useful to examine some common configurations of a device that can perform this type of ion mobility spectrometry. Consider two electrodes that are defined as either two concentric tubes or plates. The high electric field is applied for a short time, and then the low electric field is applied for a longer duration, with the average applied electric field being balanced. The non-linearity of the FAIMS system is generally attributed to the different cross-sectional areas of the ions that are drifting through the tube or between the plates. Accordingly, the method takes advantage of the different mobilities of ions in a high electric field as compared to a low electric field.
As previously mentioned, another way of describing FAIMS is to say that the separation of ions is based on the nonlinear dependence of the mobility constant with respect to the electric field intensity. The change in mobility at high electric field values appears to reflect the size of the ion, its interaction with the buffer gas, and the structural rigidity of the ion. Thus, the combination of their low field and their high field ion mobilities is used to characterize the ions in FAIMS.
It would be an advantage over the prior art to provide a new system that combines, in a single device, the techniques of ion mobility-based measurement with mass spectrometry, to thereby take advantage of the benefits that can be derived from combining the hardware required to perform both of these procedures, eliminating the step of transporting ions from one device to another, and allowing these procedures to be performed in any desired sequence, and any number of times.